The general objectives are the understanding of the hearing process in man and animals under normal and abnormal conditions. Principal methods of investigation include (1) the recording of electrophysiological responses in the ear during stimulation with sounds, (2) the determination of auditory acuity in animals by conditioning and other objective methods, and (3) a correlation of electrophysiological and behavioral results with anatomical studies of the ear. A special concern is with the lower vertebrates and the course of evolution of the vertebrate ear.